Ringing and banding, if for valid scientific research (be it conservation, systematics, population ecology, behavioural research, migration studies etc...) is acceptable, provided it is performed in a professional and ethical manner, and under the auspices of the country's relevant authorities. Much valuable information about many species has been gathered as a result of banding.
A recent example comes from the latest issue of Emu, the journal of the RAOU (Royal Australian Ornithologist's Union) where a ringing project of brown falcons (F. berigora) has, over the course of several years, worked out that previously described colour morphs and subspecies are in fact plumages that indicate age and gender of individual falcons. Other recent Australian banding projects have helped map the migration pathways and wintering grounds of several migratory waders, and satellite tracking has been used to map out the fishing grounds of albatross spp. with implications for their protection from long-line fishing.
Nick-on's comparison of netting and ringing of migratory waders suffers from comparing an activity designed to further the understanding and conservation of birds with the gratification of birders to further their own lists. Also, the size comparison between a 20cm bird and a 200cm human is a size difference of 10 times, not two orders of magnitude larger.
On the other hand, without having read your post on cats, I reckon I probably agree with you on them. I've seen too many cats with parrots, wrens, thrushes etc... in their mouth to feel the slightest compassion for them.